The present invention relates to a new process for obtaining chloroformates by phosgenating the corresponding alcohols under pressure with or without a catalyst, preferably in the absence of a catalyst.
Conventional processes consist in injecting phosgene into the alcohol, alone or in solution, under atmospheric pressure. In general, an excess of phosgene is used. The educts, consisting of a mixture of phosgene and hydrochloric acid, are inseparable under atmospheric pressure unless very low temperature condensers are used, which always results in a loss of phosgene.
The chemistry is governed by the following equation:
R(OH)n+nCOCl2 xe2x86x92R (OCOCl)n +nHCl xe2x80x83xe2x80x83(k)
In order to activate the reaction, it is necessary to employ one or more catalysts; consequently, there is numerous literature concerning these derivatives. The use of a catalyst, however, presents a number of disadvantages. Foremost among these is their cost, followed by their influence on the choice of materials, since the catalysts often make the reaction system highly corrosive. Further, the catalyst promotes the formation of by-products and the development of discoloration. Finally, it necessitates purification of the chloroformate by distillation or crystallization.
The aim of the invention is to avoid the abovementioned disadvantages that are associated, in particular, with the use of catalysts.
The invention provides a process for phosgenating monohydroxy alcohols and/or polyols to obtain the corresponding chloroformates, characterized in that the alcohol and/or polyol are/is treated in the presence or absence of solvent with a molar excess of phosgene, preferably from approximately 2 to 30 times more phosgene per hydroxyl group, at a temperature of between 0 and 200xc2x0 C. and at a pressure of between 2 and 60 bar (1 bar =105 Pa) with or without a catalyst, preferably in the absence of any catalyst. The process is generally carried out in a closed system (autogenous pressure) or in an open system (pressure regulated by partial degassing, for example). The process is generally operated continuously or semicontinuously. It is preferred to operate in an open system with partial degassing. Degassing must be carried out while ensuring that an excess of phosgene remains. This is done either by selective removal of the hydrochloric acid, while retaining the excess of phosgene and a little HCl, or by a degassing which includes the phosgene, with the latter being resupplied at the same time. The temperature is advantageously selected between 20 and 150xc2x0 C., preferably between 25 and 80xc2x0 C., while the pressure is selected preferably between 6 and 40 bar. The temperature and pressure conditions are determined by the nature of the alcohol and/or polyol and of the corresponding chloroformate, in particular by the critical point and/or decomposition point.
The advantages of the pressure phosgenation according to the invention are to be able a) to make it possible to do away with the low temperature condensers, b) to do away with solvent and/or catalyst, and c) to obtain chloroformates with little or no by-products such as carbonates and chlorides. This makes it possible to avoid final purification of the resulting chloroformate, to have a simple separation at the end of the reaction, and to reduce the cost of utilities, the advantages, in general terms, being those already discussed above and linked with the absence of catalyst.
The process according to the invention is advantageously employed for converting alcohols and/or polyols of formula R(OH)n to chloroformates R(OCOCl)n, n being an integer from 1 to 6 and R being defined as follows:
- a saturated or unsaturated, linear or branched aliphatic radical having 1 to 22 carbon atoms which is optionally substituted a) by one or more identical or different halogen atoms, b) by one or more nitro groups, or c) by at least one alkyloxy, aryl (preferably phenyl), aryloxy or arylthio group, each of these groups being unsubstituted or substituted;
- a saturated or unsaturated, linear or branched polyoxyalkylene radical which is optionally substituted by the substituents indicated above and has a molecular mass of between 200 and 6000 (with the proviso that the alcohols are liquid or can be dissolved under the reaction conditions);
- a cycloaliphatic radical having 3 to 8 carbon atoms which bears or does not bear one or more substituents selected from a) halogen atoms, b) alkyl or haloalkyl radicals, c) nitro groups and d) aryl (preferably phenyl), aryloxy or arylthio radicals, it being possible for these radicals themselves to be unsubstituted or substituted;
- an aromatic carbocyclic radical which is unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl or haloalkyl radicals (preferably CF3) having 1 to 12 carbon atoms (for example C2-C6 alkenyl, C3-C8 cycloalkyl, C4-C10 cycloalkylalkyl, C7-C10 aralkyl and C7-C10 aralkoxy), alkylthio or haloalkylthio radicals having 1 to 6 carbon atoms, alkylsulphinyl or haloalkylsulphinyl radicals having 1 to 6 carbon atoms, alkylsulphonyl or haloalkylsulphonyl radicals having 1 to 6 carbon atoms, alkyloxy or haloalkyloxy radicals having 1 to 6 carbon atoms, aryl, arylthio or aryloxy radicals, and the nitro group;
- a 5- or 6-membered aromatic or nonaromatic heterocyclic radical having one or more identical or different heteroatoms selected from oxygen, sulphur and nitrogen atoms and being unsubstituted or substituted by one or more substituents selected from halogen atoms, nitro groups, alkyl, haloalkyl, alkyloxy, haloalkyloxy, aryl, arylthio and aryloxy radicals and/or being optionally condensed with an aromatic carbocycle which itself is unsubstituted or substituted.
In general, when an aryl group (or one of its derivatives such as aryloxy or arylthio) or an aromatic carbocycle is mentioned, it should be considered, even if not stated at the time when such a radical appears, in order to lighten the present specification, that the said group or carbocycle can bear substituents selected from the group consisting of halogen atoms and alkyl, haloalkyl, alkyloxy, haloalkyloxy, alkylthio, haloalkylthio, alkylsulphinyl, haloalkylsulphinyl, alkylsulphonyl, haloalkylsulphonyl, aryl, aryloxy, arylthio and nitro radicals.
The process according to the invention is also suitable for converting mixtures of monohydroxy alcohols and/or mixtures of monohydroxy alcohols and polyols to corresponding chloroformates.
This process according to the invention is likewise characterized in that the pressure is further used to facilitate the separation of the hydrochloric acid and the phosgene in a column external to the reactor, without employing low temperature condensers which are, as has already been seen, a source of COCl2 losses. The separation hence becomes more simple, and thus more economic, than with the known processes, and leads to readily recyclable phosgene and to pure hydrochloric acid.